1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device having internal power supply voltage down-converting circuits for down-converting an external power supply voltage and generating internal power supply voltages, and more particularly, it relates to a semiconductor integrated circuit device having at least one voltage-dividing type internal power supply voltage down-converting circuit and at least one direct feedback type internal power supply voltage down-converting circuit. More specifically, the present invention relates to a structure for equalizing internal power supply voltages generated by the voltage-dividing type and the direct feedback type internal power supply voltage down-converting circuits with each other in temperature dependency.
2. Description of the Prior Art
As a semiconductor integrated circuit device is improved in degree of integration, MOS transistors (insulated gate field-effect transistors) as the components thereof are refined in response. In order to guarantee a breakdown voltage of the refined transistors, operating power supply voltages must be reduced. However, an integrated circuit device such as a semiconductor memory device must be further refined as compared with an integrated circuit such as a processor or a logic circuit, in order to implement a large storage capacity. Further, it is necessary to keep compatibility with semiconductor memory devices of old generations. Therefore, the overall system power supply voltage cannot be reduced, and a high voltage of 3.3 V, for example, is employed as the system power supply voltage in consideration of compatibility with processors and logic circuits or devices of old generations, so that the integrated circuit device such as a semiconductor memory device down-converts this external power supply voltage to 2.5 V, for example, in its interior for generating the operating power supply voltages.
FIG. 11 illustrates an exemplary structure of a conventional internal power supply voltage down-converting circuit VDCa. Referring to FIG. 11, the internal power supply voltage down-converting circuit (hereinafter simply referred to as a voltage down-converting circuit) VDCa includes a comparator CMPa for comparing a voltage VIN1 on an internal power supply line VLa with a reference voltage Vref1 and outputting a signal indicating the result of the comparison, and a current drive transistor DRa formed by a p-channel MOS transistor and connected between a power supply node ENa receiving an external power supply voltage VEX and the internal power supply line VLa for supplying a current from the power supply node ENa to the internal power supply line VLa in accordance with the signal outputted from the comparator CMPa. The comparator CMPa receives the reference voltage Vref1 at its negative input, while receiving the internal power supply voltage VIN1 on the internal power supply line VLa at its positive input. The operation is now briefly described.
When the reference voltage Vref1 is higher than the internal power supply voltage VIN1, the output signal from the comparator CMPa goes low to increase the conductance of the current drive transistor Dra, for supplying the current from the power supply node ENa to the internal power supply line VLa and increasing the level of the internal power supply voltage VIN1. When the reference voltage Vref1 is lower than the internal power supply voltage VIN1, the output signal from the comparator CMPa goes high to bring the current drive transistor DRa into an OFF state, for cutting off the current path between the power supply node ENa and the internal power supply line VLa. Namely, when the internal power supply voltage VIN1 is lower than the reference voltage Vref1, the conductance of the current drive transistor DRa is adjusted in response to the voltage difference for supplying the current from the power supply node ENa to the internal power supply line VLa. Thus, the internal power supply voltage VIN1 is held substantially at the level of the reference voltage Vref1.
FIG. 12 illustrates another exemplary structure of a conventional voltage down-converting circuit VDCb. Referring to FIG. 12, the voltage down-converting circuit VDCb includes a resistive element RE connected between an internal power supply line VLb and a node ND, a constant current source IS connected between the node ND and a ground node supplying a ground voltage VSS which is a basic voltage, a comparator CMPb for comparing the voltage on the node ND with a reference voltage Vref2, and a current drive transistor DRb formed by a p-channel MOS transistor which is connected between a power supply node ENb receiving an external power supply voltage VEX and the internal power supply line VLb for supplying a current from the power supply node ENb to the internal power supply line VLb in accordance with an output signal of the comparator CMPb. The operation of the voltage down-converting circuit VDCb shown in FIG. 12 is now briefly described.
The comparator CMPb compares the voltage on the node ND with the reference voltage Vref2. Similarly to the voltage down-converting circuit VDCa shown in FIG. 11, the conductance of the current drive transistor DRb is adjusted in accordance with the output signal of the comparator CMPb, for substantially equalizing the voltage level on the node ND with the reference voltage Vref2. In this case, therefore, an internal power supply voltage VIN2 on the internal power supply line VLb is given by V(ND)+Ixc2x7R, where V(ND) represents the voltage on the node ND, and I and R represent the current supplied by the constant current source IS and the resistance value of the resistive element RE respectively. The internal power supply voltage VIN2 is reduced through the resistive element RE to be compared with the reference voltage Vref2, thereby driving the comparator CMPb in its most sensitive region and recovering the internal power supply voltage VIN2 to a prescribed level at a high speed upon its fluctuation.
It is possible to supply the internal power supply voltages VIN1 and VIN2 of a constant voltage level as operating power supply voltages for internal circuits by down-converting the external power supply voltage VEN through the voltage down-converting circuits VDCa and VDCb shown in FIGS. 11 and 12.
FIG. 13 schematically illustrates the overall structure of a conventional semiconductor integrated circuit device IC. Referring to FIG. 13, the semiconductor integrated circuit IC includes an internal circuit #A receiving the internal power supply voltage VIN1 from the voltage down-converting circuit VDCa shown in FIG. 11 as an operating power supply voltage, and an internal circuit #B receiving the internal power supply voltage VIN2 from the voltage down-converting circuit VDCb shown in FIG. 12 as an operating power supply voltage. No high-speed operation is required to the internal circuit #A, which in turn consumes a relatively large current. On the other hand, a high-speed operation is required to the internal circuit #B, which in turn consumes a relatively small current.
The semiconductor integrated circuit IC employs the voltage down-converting circuit VDCa which can supply a large current but is not required of high-speed response and the voltage down-converting circuit VDCb which is responsive to fluctuation of the internal power supply voltage VIN2 at a high speed while supplying a relatively small current, independently of each other depending on the operational characteristics of the internal circuits #A and #B respectively.
Particularly, when the internal circuit #A consumes a large current to fluctuate the internal power supply voltage VIN1, the semiconductor integrated circuit device IC can prevent the internal power supply voltage VIN2 for the internal circuit #B from an adverse influence by the fluctuation of the internal power supply voltage VIN1 (the voltage down-converting circuits VDCa and VDCb are provided independently of each other for the different internal power supply lines VLa and VLb, thereby preventing propagation of power supply noise). Thus, it is possible to implement a semiconductor integrated circuit device stably operating at a high speed.
The direct feedback voltage down-converting circuit VDCa directly comparing the internal power supply voltage VIN1 with the reference voltage Vref1 shown in FIG. 11 and the voltage-dividing voltage down-converting circuit VDCb shifting the level of the internal power supply voltage VIN2 for comparison with the reference voltage Vref2 are different in structure and temperature dependency from each other. The comparators CMPa and CMPb and the current drive transistors DRa and DRb exhibit substantially similar temperature dependency. If the temperatures of the current drive transistors Dra and DRb increase, for example, channel resistances thereof increase to reduce the levels of the internal power supply voltages VIN1 and VIN2. Even if the output signals from the comparators CMPa and CMPb are at low levels, the current drive transistors DRa and DRb enter OFF states due to change of threshold voltages thereof.
The difference in temperature dependency is small. However, the voltage-dividing voltage down-converting circuit VDCb includes the resistive element RE for level shifting and the constant current source IS, and hence the power supply voltages VIN1 and VIN2 generated by the direct feedback voltage down-converting circuit VDCa and the voltage-dividing voltage down-converting circuit VDCb remarkably differ in temperature dependency from each other.
For example, no particular problem arises when the difference xcex94V between the internal power supply voltages VIN1 and VIN2 is small under a high temperature, as shown in FIG. 14A. If the resistive element RE is made of polysilicon and has an influence of its temperature dependency remarkable, the resistance value of the resistive element RE reduces to lower the level of the internal power supply voltage VIN2 under a low temperature. Therefore, the difference xcex94V between the internal power supply voltages VIN1 and VIN2 increases as shown in FIG. 14B, to result in extremely different operationability of the internal circuits #A and #B utilizing these internal power supply voltages VIN1 and VIN2, and no desired performance can be attained. In the internal circuits #A and #B shown in FIG. 13, for example, the operating speed of the internal circuit #B reduces as compared with that of the internal circuit #A under a low temperature. Thus, the internal circuit #B cannot operate at a high speed, and desired performance of the semiconductor integrated circuit device IC cannot be implemented.
If the voltage difference xcex94V increases in a boundary region between the internal circuits #A and #B, a malfunction may take place. It is noted that FIGS. 14A and 14B indicates that the internal power supply voltages VIN1 and VIN2 are set at the same voltage level of 2.5 V, as an example.
Consider a CMOS invertor which receives an input signal IN having the amplitude of the internal power supply voltage VIN2 and receives the internal power supply voltage VIN1 as an operating power supply voltage, as shown in FIG. 15. This CMOS invertor includes a p-channel MOS transistor PQ and an n-channel MOS transistor NQ. The internal signal IN is supplied to the gates of the MOS transistors PQ and NQ. Consider that the internal signal IN is at a high level equal to the level of the power supply voltage VIN2. If the difference xcex94V between the internal power supply voltages VIN1 and VIN2 exceeds the absolute value of the threshold voltage of the p-channel MOS transistor PQ, the p-channel MOS transistor PQ is not turned off despite the high-level internal signal IN, and a through current is caused in this CMOS invertor to increase current consumption. When the voltage difference xcex94V is large, an output signal OUT does not go low and a malfunction takes place in the internal circuit.
The difference of operational voltage dependency shown in FIGS. 14A and 14B is a mere example, and the difference xcex94V between the internal power supply voltages VIN1 and VIN2 may reduce or increase under a low or high temperature, depending on the temperature dependency of the resistive element RE and the constant current source IS included in the voltage-dividing voltage down-converting circuit VDCb. If the constant current source IS is formed by a MOS transistor having a high temperature dependency, the current suppliability of the constant current source MOS transistor reduces to lower the internal power supply voltage VIN2 under a high temperature.
In case of employing the direct feedback voltage down-converting circuit VDCa and the voltage-dividing voltage down-converting circuit VDCb, the difference xcex94V between the internal power supply voltages VIN1 and VIN2 increases in a certain temperature range due to the difference in temperature dependency therebetween, the internal circuits #A and #B remarkably differ in operational performance from each other, and therefore the performance of the semiconductor integrated circuit device IC disadvantageously reduces.
An object of the present invention is to provide a semiconductor integrated circuit device including voltage down-converting circuits having no difference in temperature dependency from each other.
Another object of the present invention is to provide a semiconductor integrated circuit device including internal voltage down-converting circuits, which stably operate in the overall temperature range.
Briefly stating, the semiconductor integrated circuit device according to the present invention utilizes a voltage employed by a direct feedback voltage down-converting circuit for generating an internal power supply voltage as a reference voltage or a comparand voltage for a voltage-dividing voltage down-converting circuit.
The semiconductor integrated circuit device according to the present invention includes a first comparator for comparing a first reference voltage with a voltage on a first internal power supply line and outputting a signal indicating the result of the comparison, a first current drive element coupled between a first power supply node receiving an external power supply voltage and the first internal power supply line for supplying a current from the first power supply node to the first internal power supply line in accordance with the signal outputted from the first comparator, a first voltage dividing circuit for dividing a voltage on a second internal power supply line by a prescribed ratio for outputting, a second voltage dividing circuit for dividing the first reference voltage by the prescribed ratio and generating a second reference voltage, a second comparator for comparing the second reference voltage with the voltage outputted from the first voltage dividing circuit and outputting a signal indicating the result of the comparison, and a second current drive element connected between a second power supply node receiving the external power supply voltage and the second internal power supply line for supplying a current from the second power supply node to the second internal power supply line in accordance with the signal outputted from the second comparator.
A reference voltage of a direct feedback voltage down-converting circuit is divided by the same ratio as that for dividing an internal power supply voltage of a voltage-dividing voltage down-converting circuit for generating a reference voltage, so that the voltage-dividing voltage down-converting circuit generates an internal power supply voltage on the basis of the divided reference voltage. Even if the temperature dependency of a voltage dividing circuit provided in the voltage-dividing voltage down-converting circuit remarkably varies, the reference voltage also varies responsively, whereby the internal power supply voltage generated by the direct feedback internal voltage down-converting circuit can be rendered substantially identical in temperature dependency to that generated by the voltage-dividing voltage down-converting circuit, and the internal power supply voltages can be stably supplied over the entire temperature range.
A second internal power supply voltage is generated with reference to the first internal power supply voltage, so that the second internal power supply voltage exhibits the same temperature dependency as that of the first internal power supply voltage employed as a reference voltage, whereby no difference is caused in temperature characteristics and the difference between the internal power supply voltages of the two voltage down-converting circuits is substantially constant over the entire temperature range.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.